Method of producing printing plates



Patented Feb. 13, 1945 METHOD OF PRODUCING PRINTING PLATES Fritz HermannHausleiter, Munich, Germany; vested in the Alien Property Custodian NoDrawing. Application September 10, 1940, Se-

rial No. 356,190. In Germany September 14,

4 Claims.

While letterpress printing as well as intaglio and printing of the imageor letters takes place in another plane than the non-printing portions,the flat or offset printing is based on' the fact that the fat printingink is repelled by the por-' tions moistened with water, or theso-called etched portions. By this etching (with salt or acidsolutions), producing a deposit on the surface of the plate or stone(generally used for flat or offset printing), these portions becomewater-carrying while the image or letters, con sisting of fat substancesor lacquers, constantly take 'up the'printing ink (the level which iscontinually moistened does not take on any ink). On the flat printingplates of known type continuous re-etching is necessary. The lattermust,

however, not corrode the fat picture. When the machine is running itfurther happens that the picture spreads or fades. The oxidation of theprinting plate sometimes causes scumming (socalled scum on the plate).The addition of etching solutions to the fountain water, often causingfading of the picture, is necessary in orderto avoid scum and to preventthat the water-carrying layer gets lost as the surface of the level isrubbed off by sandy or dusting paper. The fountain etch renews thiswater-carrying layer but it also has a corrosive effect on the sensitivestructure of the image (fat or lacquer base) so that only a small runcan be reached.

The printing metals zinc and aluminum which "up to 'the present had beengenerally used are too soft and wear ofi rapidly, the more so as theymust be grained to be sulficiently watercarrying, but the grain pointswear ofi more rapidly than the surface of a smooth plate would.Ungrained plates, however, could not be used up to 'the presentbecause'these do not sufliciently resist the tendency of the metal totake up ink, that is to get'scummy. The, possibility of using smoothplates would, however, mean a very great progress in the printingindustry as the smooth surface much clearer reproduces the image anddoes not wear off (especially if it is screened), so that the run can'beconsiderably increased.

In order to obviate the above mentioned inconveniences, it has alreadybeen proposed to make also the image of metal and to employ forthe-level a metal capable of being moistened by water, aso-calledwater-carrying metal, and for the image a metal capable of attractingoil or. fat, a so-called fat-carrying metal.

A known method of this kind provides thatthe plate or carrier metalisuniformly coated printing is based on the principle that the inking witha thin film of another metal, that then the image is applied and thatthe non-covered image portions are removed by etching down to thecarrier metal. Another proposition consists in bringing the picture insome way, in this case negatively, onto the carrier metal, and in depos-I iting galvanically another metal unto the unnon-printing portions ofwater-attracting metal,

it has already been proposed to arrange the printing portions below thelevel of the nonprinting portions in order to prevent in this mannerthat the image metal is influenced during the repeated cleaning of theplate, but detailed explanations how to do this have not yet beensuggested. The idea has also been expressed to attain by a certainselection of the two metals a diilerent capacity for carrying water orfat,

- respectively oil.

No useful result, however, has been attained by the methods proposed upto the present because the chemical nature of the combination of the twoselected metals can be never 'so highly varied that the one metal isreliably well watercarrying and the other metal fat-carrying so thatthis variation is preserv'edduring the whole printing process. Theinvention proposes an absolutelynew method for attaining this aim by inaprinting plates with one of the substances known from the flotation asso-called flotation additions .so that the moistening capability, asregards fat and oil or water, is respectively increased.

The flotation or floating dressing is based on When producing fiatprinting plates the purpose is of course different because molstenmgwith oil takes place during the printing. Consequently, one added mediumwill generally be sufficient for the method according to the invention(compare for instance Ullmann, Encyclopaedia of the Technical Chemistry,volume 1, 1928, page 796 .and following). Alkaline additions or suchwhich reduce the formation of ilakes or such which possess eii'ectssimilar to those of the oil also can be considered. The additions usedfor differential flotation and such additions which cause a chemicalalteration of the surface, as for instance sulfidizing additions, haveproved to be particularly suitable. It has further shown to be suitablein individual cases to add in fine distribution to the treating liquid(etch) an oil or the type of the flotation oils.

The treatment can be carried out with solutions suitable alloys for thelevel metal are nickelmagnesium on a copper plate or cobalt-magnesium ona zinc plate.

If a !brass plate for the image is employed and an alloy of nickel andmagnesium is used for the level, an aqueous solution of xanthogenicalkali salts and hydroferrocyanic salts, preferably at a pH of about 8to 9 can be used for the treatment according to the invention. For othermetal combinations, such as zinc with cobalt-magnesium, the same liquidcan be used. The value of the xanthogenic salts is preferablypreponderate, and the pH value is located at about 6 to 7.

For instance, the surface of a metal plate may bear a non-electricinsulating coating, such as lacquer or ink, the plate being galvanizedwith a metal of the iron group. Then follows the treatment with thesolutions according to the invention. I

The production of the plate may, however, be

' carried out in inverse manner:

of the additions in organic or inorganic solvents.

In organic solvents the oil and the addition dissolve completely, ininorganic media, especially water, the additions may be dissolved andthe oil emulsified.

For certain metal combinations, the treatment in such a solution offlotation additions is suificient, in other instances, however, it isadvisable to provide further a treatment with the socalled lithographicetches as have been used up to the present in order to make the levelwater-carrying. This etching can take place before the treatment withthe flotation additions or more advantageously after the same. Anespecially advantageous embodiment of the invention consists, however,in the simultaneous flotating and etching. This is carried out byemployment of a solution which contains both the flotation media andlithographic etches.

All chemical solutions suitable to serve as water moistening media oretches which have hitherto been .used to obtain the water-carryingcapability of the metal level or printing plates, that is for increasingthe capability for carrying water. Solutions of ferric cyanides, thatis, such solutions which contain ferroor ferricyanide ions have,however, proved to be especially suitable. They produce a much thickerand more strongly adhering film from a metal salt deposit on the levelportions than the commonly used etches, this being trueof metals of theiron group, for instance nickel and cobalt, as water-carrying metal.

The selection of the-flotation addition depends chiefly on the nature ofthe image metal which is used, however, also on the nature of the levelmetal. In every individual case an addition of the kind has to beemployed which renders the surface of the image the most capable ofoilmo-istening but which has the least possible influence on the levelmetal and does not disturb the etching effect.

The selection of suitable metal combinations depends on the existingconditions. In many cases it is especially advisable to use asfatcarrying metal a metal or an alloy of the copper group, for instancea nickel-cobalt alloy. Other A brass sheet metal plate might, forinstance, be coated with a suitably thick layer of cobalt, an image beproduced on this layer (the image resisting corrosives, for instance alacquer copy), whereupon the cobalt layer is etched through down to thebrass plate at the uncovered portions, for instance by means of chromicacid solution.

Example 1 According to the invention the image is produced in anysuitable manner in fat ink on a brass plate. This can be obtained bytransferring or by printing down, by hand-drawing, or in a similarmanner. The level, that is the unprotected parts, is then nickeled, orcoated with a deposit of, for instance, magnesium containing nickel.

The flat printing plate thus obtained is lithographically etched,preferably with an etch consisting of l to 20%, preferably 1 to 5%hydroferrocyanic potassium solution, to which alkali is added perhaps upto the pH value of 9. The plate is then placed in the machine. Afountain etch, which is suitably diluted and besides containskanthogenic light metal salt, is used. If the plate has to be washed outfor any reason, this is done with pure solvents, for instance benzene,benzol or the like, and the plate can be etched in this washed out statewith a liquid preferably of the following composition.- The liquid hasalways the property to render one of the metals, in this instance thebrass, extraordinarily receptive to fat. whereas the second metal,nickelmagnesium, is strongly etched lithogralphically and therebybecomes strongly ink-repellent.

The above described treatment and the selection of relativelynon-corroding metals for the level; for instance nickel, cobalt,eliminates the disagreeable work of gumming the plate during thestandstill of the machine or the like, which was essential when lessnon-corroding metals, for instance the hitherto used printing metalszinc and aluminum were employed.

The etch to be used for the above combination brass-nickel-magnesium iscomposed as follows:

Water ccm 1,000 Hydroferrocyanic potassium g 10-100 KOH g 2-8 Xanthate g1-4 Emulsiflable oil g 1-2 Instead of the xanthate named in this examplealso other flotation additions may be chosen according to the principlesas are known in flotation. For instance, sulfoureas such asdiphenylsulfourea or salts of the hydrogen thiocyanate acid have provedto be suitable. In this connection some examples will be given in thefollowin Example 2 A solution of the following composition is employedfor a printing plate of zinc as image metal and of nickel as levelmetal:

Water ccm 1,000 Hydroferricyanic sodium g -100 Oxalic acid g 2-8Diphenylsulfourea g l-10 if necessary 0.1% of emulsifiable oil may beadded.

Example 3 For a printing plate, the image portions of which consist ofcopper and the level portions of iron, asolution of the followingcomposition is used:

Water mm 1,000 Ammonium thiocyanate g 10-100 Xanthogenic potassium g 1-4slum, cobalt or the like is galvanically deposited.

I claim:

1. Process of producing printing plates having an image metal portionselected from the group consisting of nickel-cobalt alloy, copper, zincand brass and a level metal portion selected from the group consistingof nickel-magnesium alloy, cobalt-magnesium alloy, cobalt, nickel andiron, comprising treating said plate with a flotation addition selectedfrom the group consisting of alkali xanthates, sulfoureas and solublethiocyanates.

2. Process of producing printing plates having an image metal portionselected from the group consisting of nickel-cobalt alloy, copper, zincand brass and a level metal portion selected from the group consistingof nickel-magnesium alloy, cobait-magnesium alloy, cobalt, nickel andiron, comprising treating said plate with a flotation addition selectedfrom the group consisting of alkali xanthates, sulfoureas and solublethiocyanates and an etching solution.

3. Process of producing printing plates having an image metal portionselected from the group consisting of zinc and brass and a level metalportion selected from the group consisting of nickel, nickel-magnesiumand cobalt, comprising treating said plate with a flotation addition"comprising a sulfourea.

4. Process of producing printing plates having an image metal portion ofzinc and a level metal portion of nickel comprising treating said plateswith a solution comprising approximately 1000 cubic centimeters ofwater, 10 to grams of sodium hydroterricyanide, 2 to 8 grams of oxalicacid and 1 to 10 grams of diphenylsulfourea.

FRITZ HERMANN HAUSLEITER.

